Forming structures that include a relaxed or pseudo-relaxed layer on a substrate

ABSTRACT

A method for forming a structure that includes a relaxed or pseudo-relaxed layer on a substrate. The method includes the steps of growing an elastically stressed layer of semiconductor material on a donor substrate; forming a glassy layer of a viscous material on the stressed layer; removing a portion of the donor substrate to form a structure that includes the glassy layer, the stressed layer and a surface layer of donor substrate material; patterning the stressed layer; and heat treating the structure at a temperature of at least a viscosity temperature of the glassy layer to relax the stressed layer and form the relaxed or pseudo-relaxed layer of the structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/769,299filed Apr. 28, 2010, now U.S. Pat. No. 7,919,393, which is acontinuation of application Ser. No. 11/345,495 filed Feb. 2, 2006, nowU.S. Pat. No. 7,736,988, which is a continuation of application Ser. No.10/784,016 filed Feb. 20, 2004, now U.S. Pat. No. 7,018,909, whichclaims the benefit of provisional application 60/483,476 filed Jun. 26,2003. The entire content of each prior application is expresslyincorporated herein by reference thereto.

BACKGROUND ART

The present invention generally relates to the formation of a relaxed orpseudo-relaxed layer on a substrate. The relaxed layer may be made of amaterial selected from semiconductor materials, in order to form a finalstructure for electronics, optics or optoelectronics, such as asemiconductor-on-insulator structure.

A layer is “relaxed” if its crystalline material has a lattice parametersubstantially identical to its nominal lattice parameter, wherein thelattice parameter of the material is in its bulk equilibrium form.Conversely, a layer is “strained” if its crystalline material iselastically stressed in tension or in compression during crystal growth,such as during epitaxy, which forces its lattice parameter to besubstantially different from its nominal lattice parameter.

Methods for forming a relaxed layer on a substrate are known. A methodfor doing so includes conducting epitaxial growth of a thin layer ofsemiconductor material on a donor substrate, bonding a receiversubstrate at the thin layer; and then removing a part of the donorsubstrate. A semiconductor-on-insulator structure can thus be made. Thesemiconductive thickness consists partially of the relaxed thin layer,and the insulating layer is usually formed in an intermediate stepbetween the epitaxial and bonding steps.

The thin layer may be fabricated during an epitaxial step or duringsubsequent treatment. In the first case, it is known to use a donorsubstrate consisting of a backing substrate and a buffer layer, thebuffer layer confining plastic deformations so that the epitaxial thinlayer is relaxed from any stress. Such methods are, for example,described in published documents US 2002/0072130 and WO 99/53539.However, a buffer layer is often time consuming and costly to make. Inthe second case, the donor substrate does not comprise any buffer layerand the epitaxial step then consists of growing the thin layer to bestressed by the donor substrate. Thus, for example, a SiGe layer will begrown directly on a Si substrate that has a thickness such that the SiGelayer is globally stressed.

A first technique for relaxing the SiGe layer, notably as described inthe document of B. Hollander et al. entitled “Strain relaxation ofpseudomorphic Si_(1-x)Ge_(x)/Si(100) heterostructures after hydrogen orhelium ion implantation for virtual substrate fabrication” (in Nuclearand Instruments and Methods in Physics Research B 175-177 (2001)357-367) consists of relaxing the SiGe layer, before applying a bondingstep, by implanting hydrogen or helium ions in the Si substrate at apredetermined depth. However, relaxation rates usually obtained withthis first technique remain rather low as compared with othertechniques.

A second technique is disclosed in the document entitled “CompliantSubstrates: A comparative study of the relaxation mechanisms of strainedfilms bonded to high and low viscosity” by Hobart et al. (Journal ofElectronic Materials, vol. 29, No. 7, 2000). After removing the donorsubstrate during a removal step, heat treatment is applied for relaxingor pseudo-relaxing a layer of stressed SiGe, bonded to a BPSG glassduring the bonding step. During the heat treatment, the stressed layerthus seems to relax via the layer of glass which has become viscous dueto the treatment's temperature. However, this latter technique involvesrelaxation of the SiGe thin layer when the latter is exposed. Exposureof such a SiGe layer (exposed) to a gas atmosphere during heat treatment(such as a room RTA treatment, a sacrificial oxidization, or a recoveryanneal) may prove to be disastrous for the quality of this layer,wherein Ge contained in the layer may diffuse outwards (which may causedecomposition of the layer) and the layer may be contaminated byexternal contaminants.

Furthermore, such a SiGe layer is on the surface and may therefore haveto undergo special treatment such as finishing treatments (polishing,smoothening, oxidization, cleanings, etc.). At the present, suchtreatments for SiGe are not as effective as those for Si. This lack ofcontrol when working with SiGe causes further difficulties for making adesired structure.

The present invention now overcomes these problems.

SUMMARY OF THE INVENTION

The invention relates to methods of forming a structure that includes arelaxed or pseudo-relaxed layer on a substrate. The method includes thesteps of growing an elastically stressed layer of semiconductor materialon a donor substrate; forming a glassy layer of a viscous material onthe stressed layer; removing a portion of the donor substrate to form astructure that includes the glassy layer, the stressed layer and asurface layer of donor substrate material; patterning the stressedlayer; and heat treating the structure at a temperature of at least aviscosity temperature of the glassy layer to relax the stressed layerand form the relaxed or pseudo-relaxed layer of the structure.

Preferably, the patterning comprises etching islands in the stressedlayer to contribute to relaxation of the stressed layer during the heattreating. Advantageously, components can be formed on the islands. Thesecomponents can be formed after forming the relaxed or pseudo-relaxedlayer, or during or in continuity with the heat treating.

Often, it is useful to apply an epitaxial growth process to provide atleast one epitaxial layer on the structure. The epitaxial growth processcan provide at least one epitaxial layer by applying one or more of a aSiGe or SiGeC layer, or of a stressed Si or SiC layer, or successiveepitaxial growths of SiGe or SiGeC layers or of alternately stressed Sior SiC layers in order to form a multilayer structure. Preferably, thesurface layer is removed before providing at least one epitaxial layeron the structure. When components are to be applied to the structure,these can be applied upon the stressed layer, the relaxed orpseudo-relaxed layer, or upon the epitaxial layer. Thereafter, one ormore finishing treatments can be applied to the multilayer structure toimprove properties.

The stressed layer is preferably a material of Groups III-V or II-VIwith SiGe as an illustrative example. 12. The material of the glassylayer is one that becomes viscous at a certain viscosity temperature ofabove about 900° C.

The method can include bonding a receiver substrate to the structure toform a second structure before removing part of the donor substrate andforming a third structure comprising the receiver substrate, the relaxedor pseudo-relaxed layer, the glassy layer and the surface layer. Theglassy layer may be formed on the receiving substrate prior to bondingwith the stressed layer. If desired, a bonding layer typically ofsilicon dioxide can be applied onto at least one of the patterned layeror the receiver substrate prior to bonding. A zone of weakness can beprovided in the donor substrate so that the donor substrate can bedetached along the zone of weakness. The donor substrate can befabricated by forming a porous layer on a crystalline carrier substrateand growing a crystalline layer on the porous layer, such that theporous layer comprises the zone of weakness of the donor substrate. Inthis embodiment, the donor substrate can be detached along the weakenedzone by at least one of chemical etching or mechano-chemical etching.Alternatively, the zone of weakness is formed by implanting atomicspecies in the donor substrate so that the donor substrate can bedetached along the weakened zone by applying thermal or mechanicalenergy.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, objects and advantages of the present invention willbecome more apparent upon reading the following detailed description ofthe preferred methods thereof, given as non-limiting examples, and madewith reference to the appended drawings wherein:

FIGS. 1 a-1 i illustrate the different steps of a first method accordingto the invention;

FIGS. 2 a-2 i illustrate the different steps of a second methodaccording to the invention;

FIGS. 3 a-3 i illustrate the different steps of a third method accordingto the invention;

FIGS. 4 a-4 i illustrate the different steps of a fourth methodaccording to the invention;

FIGS. 5 a-5 h illustrate the different steps of a fifth method accordingto the invention;

FIGS. 6 a-6 h illustrate the different steps of a sixth method accordingto the invention; and

FIG. 7 is an illustration of a structure having an exposed strainedlayer as provided, e.g., by the processes of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present method overcomes the difficulties evident in the prior artby providing, according to a first aspect, a method of forming a relaxedor pseudo-relaxed layer on a substrate. The relaxed layer is asemiconductor material. The method includes growing an elasticallystressed semiconductor layer on a donor substrate, and forming, on thestressed layer or on a receiving substrate, a glassy layer consisting ofa viscous material that has an associated viscosity temperature. Thetechnique further includes bonding the receiving substrate to thestressed layer via the glassy layer, removing a portion of the donorsubstrate so as to form a structure that includes the receivingsubstrate, the glassy layer, the stressed layer, and the unremovedportion of the donor substrate which forms a surface layer. Lastly, thestructure is heat treated at a temperature close to or higher than theviscosity temperature.

Implementations also relate to structures obtained after utilizing themethod of forming a relaxed or pseudo-relaxed layer on a substrate. Anembodiment of such a structure includes a substrate, a first glassylayer on top of the substrate, a semiconductor layer on top of the firstglassy layer, and a second glassy layer on top of the semiconductorlayer, wherein the semiconductor layer, after transfer to a receivingsubstrate, forms a buried layer thereon. Another structure includes alayer of a semiconductor material having a top surface; a first glassylayer on the top surface of the substrate; a semiconductor layer on thefirst glassy layer; a second glassy layer on the semiconductor layer;and a receiving substrate, wherein the second glassy layer forms aburied layer on the receiving substrate. Yet another structure includesa receiving substrate having a top surface; a glassy layer on the topsurface of the receiving substrate; and a relaxed Si_(1-x)Ge_(x) layeron the glassy layer. Additional layers may be provided on the relaxedSi_(1-x)Ge_(x) layer, such as another glassy layer, if desired.

The buried layer of the structure may be elastically stressed, or may berelaxed or pseudo-relaxed, and may be made of a Si_(1-x)Ge_(x) material.Another semiconductor layer may be interposed between the buried layerand the second glassy layer, or may be interposed between the firstglassy layer and the buried layer. Further, at least one of the firstand second glassy layers may be made of a SiO₂ material.

A layer of Si stressed by a relaxed or pseudo-relaxed SiGe layer isuseful for providing desirable properties in these structures, such as acharge carrier mobility of the order of 100%, larger than that presentwithin a relaxed Si layer.

Other features of the method for forming a relaxed or pseudo-relaxedlayer on a substrate include applying a controlled treatment afterremoving the portion of the donor substrate. The controlled treatmenttransforms at least a portion of the surface layer into a viscousmaterial to form a second glassy layer having an associated secondviscosity temperature. Further, the method may include heat treating thestructure while forming or after forming the second glassy layer. Thesecond glassy layer may thereafter be removed. A crystal growing stepcan also be advantageously applied to the structure, using a selectedsemiconductor material.

The technique can also include forming a glassy layer by growing asemiconductor layer on the stressed layer, and performing a controlledtreatment in order to transform at least a portion of the layer into aviscous material having a particular viscosity temperature. The glassylayer can be electrically insulating and the structure can be asemiconductor-on-insulator structure, the semiconductive thickness ofwhich includes the stressed layer which has been relaxed orpseudo-relaxed during the heating step.

According to a second aspect, the method provides a structure forforming a relaxed or pseudo-relaxed layer on a substrate. The structureincludes a substrate, a first glassy layer, a buried layer of materialselected from semiconductor materials, and a second glassy layer.

The present invention therefore pertains to forming a relaxed orpseudo-relaxed useful layer on a substrate. It also pertains to formingon the relaxed or pseudo-relaxed layer, a useful layer of stressedmaterial. A “useful layer” is a layer intended to receive components forelectronics, optics, or optoelectronics during subsequent treatments.

The present method also protects the layer to be relaxed orpseudo-relaxed from the atmosphere surrounding the structure in which itis contained, throughout the application of the method and especiallyduring heat treatments. Such operation prevents at least one of theatomic species of the material from being able to diffuse.

The present method also permits application of different surfacefinishing techniques onto the desired structure during fabricationwithout damaging the quality of the layer to be relaxed orpseudo-relaxed. This can notably be achieved in the particular case whenthe layer to be relaxed or pseudo-relaxed is Si_(1-x)Ge_(x), and whenthe use of different processing techniques on the structure, usuallyapplied on Si structures or layers, is desired.

An implementation of the method is described with reference to FIGS. 1 ato 1 i. FIG. 1 a shows a source wafer 10 that consists of a donorsubstrate 1 and a stressed Si_(1-x)Ge_(x) layer 2. In a firstconfiguration, the donor substrate 1 consists entirely ofmonocrystalline Si with a first lattice parameter. Advantageously, thedonor substrate 1 is made by Czochralski growth. In a secondconfiguration, the donor substrate 1 is a pseudo-substrate comprising anupper Si layer (not illustrated in FIG. 1), exhibiting an interface withthe stressed layer 2 and having a first lattice parameter at itsinterface with the stressed layer 2. Advantageously, the first latticeparameter of the upper layer is the nominal lattice parameter of Si, sothat the latter is in a relaxed state. The upper layer further has asufficiently large thickness so as to be able to impose its latticeparameter to the overlying stressed layer 2, without the lattersubstantially influencing the crystalline structure of the upper layerof the donor substrate 1.

Whichever configuration is selected, the donor substrate 1 has acrystalline structure with a low density of structural defects, such asdislocations. Preferably, the stressed layer 2 only consists of a singlethickness of Si_(1-x)Ge_(x). The Ge concentration in this stressed layer2 is preferably higher than 10%, i.e. an x value greater than 0.10. AsGe has a larger lattice parameter than Si by about 4.2%, the selectedmaterial for forming this stressed layer 2 thus has a second nominallattice parameter which is substantially larger than the first latticeparameter. The formed stressed layer 2 is then elastically stressed incompression by the donor substrate 1, i.e. it is stressed so as to havea lattice parameter substantially less than the second lattice parameterof the material of which it is made, and therefore has a latticeparameter close to the first lattice parameter. Preferably, the stressedlayer 2 further has a substantially constant composition of atomicelements.

Advantageously, the stressed layer 2 may be formed on the donorsubstrate 1 by crystal growth, such as by epitaxy by using knowntechniques such as for example, LPD, CVD and MBE (respectiveabbreviations of Liquid Phase Deposition, Chemical Vapor Deposition, andMolecular Beam Epitaxy) techniques. In order to obtain such a stressedlayer 2, without too many crystallographic defects, such as for examplepoint defects or extended defects such as dislocations, it isadvantageous to select the crystalline materials forming the donorsubstrate 1 and the stressed layer (in the vicinity of its interfacewith the backing substrate 1) so that they have a sufficiently smalldifference between their first and their second respective nominallattice parameters. For example, this lattice parameter difference istypically between about 0.5% and about 1.5%, but may also have largervalues. For example, Si_(1-x)Ge_(x) with x=0.3 has a nominal latticeparameter larger than Si by about 1.15%.

However, it is preferable that the stressed layer 2 have a substantiallyconstant thickness, so that it has substantially constant intrinsicproperties and/or facilitates the future bonding with a receiversubstrate (as illustrated in FIG. 10.

In order to prevent relaxation of the stressed layer 2, or occurrence ofinternal plastic type deformations, the thickness of the latter shouldfurther be less than a critical thickness for elastic stress. Thiscritical elastic stress thickness depends mainly on the materialselected for the stress layer 2 and on the lattice parameter differencewith the donor substrate. But it also depends on growth parameters suchas the temperature at which it has been formed, on nucleation sitesformed during epitaxial growth, or on the growth techniques used (forexample CVD or MBE).

Examples of critical thickness values for Si_(1-x)Ge_(x) layers can befound by reference to the document entitled “High-mobility Si and Gestructures” by Friedrich Schaffler (“Semiconductor Science Technology”12 (1997) 1515-1549). Concerning other materials, one skilled in the artcan easily refer to state of the art publications in order to determinethe value of the critical elastic stress thickness of a selectedmaterial for the stressed layer 2 formed on the donor substrate 1. Thus,a Si_(1-x)Ge_(x) layer with x between 0.10 and 0.30 has a typicalthickness between 200 Å and 2,000 Å, preferably between 200 Å and 500 Åby notably adapting the growth parameters. Once formed, the stressedlayer 2 therefore has a lattice parameter substantially close to that ofits growth substrate 1 and exhibits internal elastic stresses incompression.

With reference to FIG. 1 c, a glassy layer 4 is formed on the stressedlayer 2 according to a first embodiment. The material making up theglassy layer 4 becomes viscous when a viscosity temperature T_(G) isreached. Advantageously, the material of the glassy layer 4 may be ofone of the following materials: BPSG, SiO₂, SiON. When a SiO_(x)N_(y)glassy layer 4 is formed, the value of y may advantageously be varied inorder to change the viscosity temperature T_(G) which is substantially afunction of the nitrogen composition for this material. Thus, by growinga composition thereon, it is now possible to change the T_(G) of theglassy layer 4 typically between a T_(G) of the order of that of SiO₂(which may vary around 1,150° C.) and a T_(G) of the order of that ofSi₃N₄ (which is higher than 1,500° C.). A large T_(G) range may therebybe covered by varying y. The T_(G) values of the glassy layer 4, if theyessentially depend on the material of the glassy layer, may alsofluctuate according to the conditions under which the glassy layer wasformed. In an advantageous scenario, the conditions for forming theglassy layer 4 may thereby be adapted in a controlled manner in order toselect a T_(G) “à la carte”. Deposition parameters such as temperature,duration, dosage and potential of the gas atmosphere, and the like, maythus be varied. Further, doping elements may be added to the maingaseous elements contained in the vitreous atmosphere, such as boron andphosphorus which may have the property of reducing T_(G).

It is important that the stressed layer 2 be covered with the glassylayer 4 before germanium contained in the stressed layer 2 is able todiffuse into the atmosphere, and before the stressed layer 2 iscontaminated significantly, and before the surface of the stressed layer2 becomes reactive in an uncontrollable way. This last condition mayoccur when the whole undergoes heat treatment at high temperature, suchas an RTA type annealing treatment or a sacrificial oxidizationtreatment.

In an advantageous embodiment of the glassy layer 4, the following stepsare applied onto the stressed layer 2. With reference to FIG. 1 b, asemiconductor material layer 3 is grown on the stressed layer 2. Next,with reference to FIG. 1 c, a controlled treatment is applied totransform at least a portion of the layer formed in the first step intoa viscous material, by heating to a viscosity temperature, for example,to thereby form the glassy layer 4. Advantageously, the materialselected for the layer 3 is Si so that the stress level of the stressedlayer 2 will not be changed. The thickness of the layer 3 that is formedis typically between about 5 Å and about 5,000 Å, and more particularlymay be between about 100 Å and about 1,000 Å.

For the same reasons explained above, crystal growing during the growthstep of the layer 3 is preferably applied before diffusion of Ge. Thatis, shortly after the formation of the stressed layer 2 if thetemperature for forming the stressed layer 2 is maintained, or a rise intemperature subsequent to a fall in temperature to room temperaturehaving been caused immediately after forming the stressed layer 2.

The preferred method for growing layer 3 is in situ growth directly incontinuation of the growth of the stressed layer 2. The growth techniqueused may be an epitaxy LPD, CVD or MBE technique. The glassy layer 4 maybe made by heat treatment under an atmosphere with a predeterminedcomposition.

Thus, a Si layer 3 may undergo a controlled heat oxidization treatmentin order to transform this layer 3 into a SiO₂ glassy layer 4. Duringthe latter step, it is important to accurately control the parameters ofthe oxidization treatment (such as temperature, duration, oxygenconcentration, the amounts of other gases in the oxidizing atmosphere,etc.) in order to control the oxide thickness and to stop oxidization inthe vicinity of the interface between both layers 2 and 3. For suchthermal oxidization, a dry oxygen or steam atmosphere will preferably beused at a pressure equal to or larger than 1 atm. Preferably, theoxidization duration will then be varied in order to control theoxidization of layer 3. However, this control may be made by varying oneor several other parameters, either in combination or not, with the timeparameter. If necessary, reference may be made to U.S. Pat. No.6,352,942 for more details concerning an embodiment of such a SiO₂glassy layer 4 on a SiGe layer.

According to a second embodiment of the glassy layer 4, and as areplacement for the growth and controlled treatment steps illustrated byFIGS. 1 b and 1 c, respectively, a deposition of atomic species may beapplied by means for depositing atomic species on the stressed layer 2.In a first case, atomic species consisting of the glassy material willbe deposited directly. Thus, for example, SiO₂ molecules may bedeposited in order to form the SiO₂ glassy layer 4. In this second case,the following operations will be applied:

-   -   deposition of amorphous Si atomic species to form an amorphous        Si layer; and then:    -   thermal oxidization of this amorphous Si layer to thereby form        an SiO₂ glassy layer 4.

Whichever one of these deposition cases is selected, the deposition ofthe atomic species should be made before diffusion of Ge, and beforecontamination and uncontrolled surface reactivation of the stressedlayer 2. Uncontrolled surface reactivation may occur if the stressedlayer 2 remains at a high temperature.

FIGS. 1 d, 1 e and 1 f illustrate steps for removing the stressed layer2 and the glassy layer 4 from the donor substrate 1 in order to transferthem onto a receiving substrate 7. For this purpose, the method appliesa technique consisting of two successive main steps:

-   -   bonding the receiving substrate 7 to the glassy layer 4; and    -   removing a portion of the donor substrate 1.

FIG. 1 i shows application of the bonding. But before bonding, anoptional step for forming a bonding layer on at least one of the twosurfaces to be bonded may be applied, this bonding layer having bindingproperties at room temperature or at higher temperatures. Thus, forexample, forming a SiO₂ layer may improve the quality of the bond,notably if the other surface to be bonded is SiO₂ or Si. This SiO₂bonding layer is then advantageously made by depositing SiO₂ atomicspecies, or, if the surface of the latter is in Si, by thermaloxidization of the surface to be bonded.

The surfaces to be bonded may be advantageously prepared before bondingin order to make the surfaces as smooth and as clean as possible.Suitable chemical treatments for cleaning the surfaces to be bonded maybe applied, such as weak chemical etchings, an RCA treatment, ozonebaths, rinses, etc. Mechanical or mechanical/chemical treatments mayalso be applied such as polishing, abrasion, CMP (Chemical MechanicalPlanarization) or atomic species bombardment.

The bonding operation as such is carried out by bringing the surfaces tobe bonded into contact with one another. Bonding linkages are preferablyof a molecular nature wherein the hydrophilic properties of the surfacesto be bonded are utilized. In order to impart or enhance the hydrophilicproperties of these surfaces, both structures may be dipped in baths orotherwise treated before bonding, for example, they could be rinsed withdeionized water.

An annealing step may further be applied to reinforce the bondinglinkages, for example, by changing the nature of the bonding linkages,such as covalent linkages or other linkages. Thus, if the glassy layer 4is made of SiO₂, annealing may enhance the bonding linkages, especiallyif a SiO₂ bonding layer has been formed prior to bonding to thereceiving substrate 7.

If further details regarding bonding techniques are needed, referencemay be made to the document entitled “Semiconductor Wafer Bonding”(Science and technology, Interscience Technology) by Q. Y. Tong, U.Gosele and Wiley.

Once the layers are bonded, material may be removed by separating aportion of the donor substrate 1 at a weakened area 6 present in thedonor substrate 1 by supplying energy. With reference to FIGS. 1 d and 1e, the weakened area 6 is an area substantially parallel to the bondingsurface, and it has a linkage weakness between the lower portion 1 a ofthe donor substrate 1 and the upper portion 1 b. The weakness area maybe broken to separate the upper portion 1B from the lower portion 1Awhen thermal or mechanical energy is supplied. According to a firstembodiment of the weakened zone or area 6, a technique called SMART-CUT®is applied that first includes implanting an atomic species into thedonor substrate 1, at the weakened area 6. The implanted species may behydrogen, helium, a mixture of both of these species or otherlightweight species. The implantation preferably occurs just beforebonding. The implantation energy is selected so that the species that isimplanted travels through the surface of the glassy layer 4, across thethickness of the glassy layer 4, across the thickness of the stressedlayer 2, and to a predetermined depth or thickness of the upper portion1 b of the receiving substrate 1. Implantation into the donor substrate1 is preferably sufficiently deep so that the stressed layer 2 does notsuffer any damage during the detaching step from the donor substrate.The implant depth in the donor substrate is thus typically about 1,000Å.

The weakness of the linkages in the weakened area 6 mainly depends uponthe selection of the dosage of the implanted species. The dosage istypically between about 10¹⁶ cm⁻² and 10¹⁷ cm⁻² and more specificallybetween about 2.10¹⁶ cm⁻² and about 7.10¹⁶ cm⁻². Detachment of theweakened area 6 is then usually carried out by supplying mechanicaland/or thermal energy. For more details concerning the SMARTCUT® method,reference can be made to the document entitled “Silicon-On-InsulatorTechnology: Materials to VLSI, 2^(nd) edition” by J.-P. Colinge, editedby Kluwer Academic Publishers, pp. 50 and 51.

According to a second embodiment, a technique that is described in U.S.Pat. No. 6,100,166 may be applied to form the weakened area 6. Theweakened layer 6 is made before forming the stressed layer 2 and duringthe formation of the donor substrate 1. The weakened layer may be formedby:

-   -   forming a porous layer on a Si backing substrate 1A;    -   growing a Si layer 1B on the porous layer.

The backing substrate 1A, porous layer and Si layer 1B form the donorsubstrate 1, and the porous layer forms the weakened area 6 of the donorsubstrate 1. Detachment can occur by supplying thermal and/or mechanicalenergy at the porous weakened area 6, to detach the backing substrate 1Afrom the layer 1B.

The techniques for removing material at a weakened area 6, achievedaccording to one of the two non-limiting embodiments above, enables arapid removal of a large portion of the donor substrate 1. Suchtechniques also permit reuse of the removed portion 1A of the donorsubstrate 1, for example, to form another donor substrate that could beused, for example, according to the present method. Thus, a stressedlayer 2 may be reformed on the portion 1A that has been removed, andanother optional portion of a donor substrate and/or other layers mayalso be applied, preferably after polishing the surface of the portion1A.

With reference to FIG. 1 f, after separating the remaining portion 1Bfrom the removed portion 1A of the donor substrate 1, a finishing stepcan be applied to enable the remaining portion 1B to be removed.Finishing techniques such as polishing, abrasion, CMP planarization, RTAthermal annealing, sacrificial oxidization, chemical etching, can betaken alone or in combination, and may be applied for removing theportion 1B and for perfecting stacking (strengthening the bondinginterface, removal of bumps, curing defects, etc.). Advantageously, atleast at the end of finishing a step, the removal includes selectivechemical etching, either combined or not with mechanical means. Thus,solutions based on KOH, NH₄OH (ammonium hydroxide), TMAH, EDP or HNO₃,or solutions presently investigated which combine agents such as HNO₃,HNO₂, H₂O₂, HF, H₂SO₄, H₂SO₂, CH₃COOH, H₂O₂ and H₂O (as explained indocument WO 99/53539, page 9) may advantageously be used for selectivelyetching the Si portion 1B relative to the stressed Si_(1-x)Ge_(x) layer2.

After the bonding step, another technique could be applied to remove aportion of the donor substrate 1 that does not use a weakened area. Thistechnique consists of applying chemical and/or mechanical/chemicaletching. For example, optional selective etchings for the material(s) tobe removed from the donor substrate 1 may be applied according to anetch-back type method. This technique consists of etching the donorsubstrate 1 from the back, i.e. from the free face of the donorsubstrate 1. Wet etchings may be applied that apply etching solutionssuitable for the materials to be removed. Dry etchings may also beapplied for removing material, such as plasma or spray etchings.Etching(s) may further only be chemical or electrochemical orphotochemical. Etching(s) may be preceded or followed by mechanicalabrasion of the donor substrate 1, such as grinding, polishing,mechanical etching or spraying of atomic species. The etching(s) may beaccompanied by mechanical abrasion, such as an optional polishing stepcombined with the action of mechanical abrasives using, for example, aCMP method.

All the aforementioned techniques for removing material from the donorsubstrate 1 are provided by way of example, but do not limit the presentmethod. The removal method extends to all types of techniques capable ofremoving material from the donor substrate 1, in accordance with thepresent method.

With reference to FIG. 1 f, a portion 1B of the donor substrate 1 ispreserved after removal. The stressed layer 2 is buried and thusprotected from the external atmosphere. Regardless of which technique isused for removing material, selected from the techniques alreadydiscussed or from other known techniques, a surface finishing step forthe remaining portion 1B of the donor substrate 1 may be advantageouslyapplied. The finishing step may include selective chemical etching, orCMP polishing, or heat treatment, or bombardment with atomic species orany other smoothing technique.

Thus, after applying a step for removing material that included using aSMART-CUT® type technique, a smoothing treatment can be used, such asone of the following treatments:

-   -   polishing in order to obtain a thickness of between about 200 Å        to about 800 Å;    -   Ar/H₂ RTA fast annealing followed by polishing in order to        obtain a thickness of between about 200 Åto about 800 Å;    -   a single fast RTA annealing; or    -   Ar/H₂ oven annealing.

These finishing treatments are particularly suitable for application toa Si surface (of the remaining portion 1B of the donor substrate 1). Itis noted that if the SiGe stressed layer 2 had been exposed, it wouldhave been difficult to apply such techniques without deterioration ofthe stressed layer 2, as these techniques do not work well for SiGe.Thus, it is an advantage of the above described method that the surfaceof the Si surface layer 1B can be efficiently smoothed after detachment.

With reference to FIG. 1 f, after removal of the material, a structureis obtained that includes the receiving substrate 7, the glassy layer 4,the stressed layer 2 and a Si surface layer 1B (which represents theremaining portion of the donor substrate 1). The stressed layer 2 isthus substantially protected from the outside environment by theoverlying surface layer 1B and the underlying glassy layer 4.

According to an alternative method, the surface layer 1B is preserved asis. However, with reference to FIG. 1 g, a second glassy layer 8 isformed at the surface of the structure consisting of a viscous materialusing a treatment having a second viscosity temperature to form it. Theselected material for the second glassy layer 8 may, for example, be oneof the following materials: SiO₂, BPSG, SiO_(x)N_(y). This second glassylayer 8 is preferably formed by transforming the surface layer 1B into aglassy layer, by means of a suitable controlled treatment. Thus, thesecond glassy layer 8 may be created by using a heat treatment under anatmosphere having a predetermined composition. Thus, the Si surfacelayer 1B may undergo a controlled thermal oxidization treatment in orderto transform this surface layer into a SiO₂ glassy layer 8.

During the latter step, it is important to accurately control thevarious parameters of the oxidizing treatment (such as the temperature,the duration, the oxygen concentration, the other gases in the oxidizingatmosphere, etc.) in order to control the thickness of the oxide layerthat is formed, and to stop oxidization in the vicinity of the interfacebetween the layers 2 and 1B. A dry oxygen or steam atmosphere willpreferably be used for such thermal oxidization, at a pressure equal toor larger than 1 atmosphere (atm), at a temperature between about 500°C. and about 1,050° C. The duration of oxidization will preferably bevaried so as to control the oxidization of the surface layer 8. However,control may also be accomplished by varying one or several of the otherparameters, either combined with or separate from the time parameter.

Referring to FIG. 1 g, heat treatment is applied at a temperature closeto or higher than the viscosity temperature. The main purpose of theheat treatment is to relax the stresses in the stressed layer 2. Heattreatment at a temperature higher than or around the viscositytemperature T_(G) of the glassy layer 4 will cause the surface layer tobecome viscous, which will allow the stressed layer to relax at itsinterface with the glassy layer 4, resulting in decompression of atleast part of its internal stresses. Thus, if the glassy layer 4 is anSiO₂ layer created by thermal oxidization, heat treatment at a minimumof about 1,050° C., and preferably at about a minimum of 1,200° C. for apredetermined duration, will cause relaxation or pseudo-relaxation ofthe stressed layer 2. The heat treatment typically lasts between a fewseconds and several hours.

The relaxation of the stressed layer 2 is achieved without the stressedlayer 2 coming into with the outside world, unlike when conventionalmethods are used, by preventing diffusion of Ge. The stressed layer 2therefore becomes a relaxed layer 2′.

Other effects of the heat treatment on the structure may be sought, inaddition to the relaxation of the stressed layer 2. For example, anotherreason for using heat treatment may be to anneal to strengthen the bondbetween the receiving substrate 7 and the glassy layer 4. In fact,because the temperature selected for heat treatment is higher than oraround the viscosity temperature of the glassy layer 4, the latterhaving temporarily become viscous, strong adhesion linkages may begenerated with the receiving substrate 7. Thus, again taking the exampleof bonding between the SiO₂ glassy layer 4 and the receiving substrateon which a SiO₂ bonding layer has been applied, the viscosities of bothof the layers in contact will generate particularly strong covalentlinkages.

Another purpose for applying heat treatment is to form the second SiO₂glassy layer 8 by thermal oxidization. It may be desirable to form thisglassy layer 8 during or immediately after using heat treatment to relaxthe stressed layer 2, by simultaneously injecting oxygen into an oven,or else by following that heat treatment with another heat cycle.

As shown in FIG. 1 g, a structure 20 is obtained that includes theglassy layer 8, a relaxed Si_(1-x)Ge_(x) layer 2′, a glassy layer 4, anda receiving substrate 7. The relaxed Si_(1-x)Ge_(x) of layer 2′ isthereby protected from the outside by the adjacent glassy layers 4 and8. In order to expose the relaxed Si_(1-x)Ge_(x) layer 2′, it is thensufficient to remove the glassy layer 8, for example, by means of asuitable chemical treatment. Thus, if the glassy layer 8 is made ofSiO₂, the structure 20 will advantageously be treated with hydrofluoricacid HF in order to remove SiO₂ from the glassy layer 8.

With reference to FIG. 1 h, a structure 30 is formed including a relaxedSi_(1-x)Ge_(x) layer 2′, a glassy layer 4, and a receiving substrate 7.This structure 30 is a SGOI structure (Silicon Germanium On Insulator)if the glassy layer 4 is electrically insulating, such as for example aSiO₂ glassy layer 4. The relaxed Si_(1-x)Ge_(x) layer 2′ of thisstructure advantageously has a surface with a surface roughnesscompatible with growth of another crystalline material. A surfacetreatment such as a light polishing, suitable for Si_(1-x)Ge_(x), mayoptionally be applied in order to improve surface properties.

With reference to FIG. 1 i, an optional step of the present methodincludes growing a Si layer 11 on the relaxed Si_(1-x)Ge_(x) layer 2′.The Si layer is applied with a thickness substantially less than thestress critical thickness of the material of which it consists, and itis therefore stressed by the relaxed Si_(1-x)Ge_(x) layer 2′. Thus, astructure consisting of a stressed Si layer, a relaxed Si_(1-x)Ge_(x) 2′layer, a glassy layer 4, and a receiving substrate 7 is obtained. Thisstructure 40 is a Si/SGOI structure if the glassy layer 4 iselectrically insulating, such as for example a SiO₂ glassy layer 4.

Alternatives of the present method are presented with reference to FIGS.2 a-2 i, FIGS. 3 a-3 i, and FIGS. 4 a-4 i.

With reference to FIGS. 2 a-2 i, and more particularly to FIG. 2 g, themethod is generally the same as that described with reference to FIGS. 1a-1 i, except for the step for transforming the surface layer 1B into asecond glassy layer 8. In this case, a different method is applied sothat only a portion of the surface layer 1B is transformed. Thus, thereexists a remainder or intermediate layer 9 of the Si surface layer 1Bbetween the second glassy layer 8 and the stressed layer 2. Withreference to FIG. 2 h, this intermediate layer 9 is preserved after heattreatment for relaxing the stressed layer 2. The intermediate layer 9 isadvantageously preserved with a thickness less than the stress criticalthickness so that it is stressed subsequently by the relaxed layer 2′.

With reference to FIG. 2 i, growing a Si layer may be resumed on theintermediate layer 9 in order to form a stressed Si layer 11substantially identical to that of FIG. 2 i. A smoothening step could beapplied to the growth surface by means of one of the techniques alreadydiscussed before growth of silicon, in order to improve the quality ofthe crystal growth.

If heat treatment is applied to relax the stresses of the stressed layer2 at a higher than standard temperature and for longer than a standardduration, then the Ge diffuses into Si and the Ge contained in thestressed layer 2 may diffuse into the intermediate layer 9. Thus, it ispreferable to apply the relaxation of the stressed SiGe layer 2 beforeresuming epitaxial growth of the stressed Si layer 11. However, incertain other cases, this diffusion effect may be sought if it issuitably controlled. Thus, diffusion may be controlled in such a waythat the Ge species are uniformly distributed throughout both layers 2and 9, forming a unique Si_(1-x)Ge_(x) layer with a substantiallyuniform Ge concentration. A discussion of this latter point can be foundin U.S. Pat. No. 5,461,243 at column 3, lines 48-58.

Referring to FIGS. 3 a-3 i, and more particularly to FIG. 3 c, themethod illustrated is generally the same as the one described withreference to FIGS. 1 a-1 i, except for the step of transforming a layer3 into a glassy layer 4 which is applied so that only a portion of thelayer 3 is transformed. Thus, a portion of the Si layer 3 remainsinserted between the glassy layer 4 and the stressed layer 2, forming aninserted layer 5. This inserted layer 5 is created to have a thicknessof about 10 nm, in any case much less than that of the stressed layer 2.During heat treatment for relaxing the stress of the stressed layer 2,the latter will want to reduce its internal elastic stress energy byutilizing the viscosity properties of the glassy layer 4 which hasbecome viscous. Further, because the inserted layer 5 has a smallthickness relatively to the overlying stressed layer 2, the stressedlayer 2 will impose its relaxation requirement on the inserted layer 5.The stressed layer 2 thereby forces the inserted layer 5 to be at leastpartially under stress. The stressed layer 2 then becomes an at leastpartially relaxed layer 2′. The relaxed inserted layer 5 then becomes astressed inserted layer 8′. A discussion of the latter point can befound in U.S. Pat. No. 5,461,243 at column 3, lines 28-42.

With reference to FIG. 3 h, the stressed inserted layer 5′ is preservedafter the heat treatment for relaxing the stressed layer 2. Thestructure that is formed consists of a relaxed Si_(1-x)Ge_(x) layer, astress Si layer, a glassy layer 4, and a receiving substrate 7. Thisstructure 30 is a SG/SOI structure if the glassy layer 4 is electricallyinsulating, such as, for example, a SiO₂ glassy layer 4. It is thenpossible to optionally remove, for example by selective chemical etchingbased on HF:H₂O₂:CH₃COOH (selectivity of about 1:1,000), the relaxedSi_(1-x)Ge_(x) layer 2′, in order to finally obtain a structureconsisting of a stressed Si layer, a glassy layer 4, and a receivingsubstrate 7. This structure is a stressed SOI structure if the glassylayer 4 is electrically insulating, such as, for example, a SiO₂ glassylayer 4.

Instead of applying chemical etching, it is possible to resume growth ofa Si layer on the relaxed layer 2′ a shown in FIG. 3 i, so as to form astressed Si layer 11. The resulting structure 40 consists of a stressedSi layer, a relaxed Si_(1-x)Ge_(x) layer, a stressed Si layer, a glassylayer 4, and a receiving substrate 7. This structure 40 is a Si/SG/SOIstructure, if the glassy layer 4 is electrically insulating, such as,for example, a SiO₂ glassy layer 4. In a particular scenario, if heattreatment for relaxing the stresses of the stressed layer 2 is carriedout at a temperature that is higher than a standard temperature and forlonger than a standard duration, such that Ge diffuses into Si, the Gecontained in the stressed layer 2 may diffuse into the stressed insertedlayer 5′. Thus, it is preferable to apply the relaxation of the stressedSiGe layer 2 before resuming epitaxy of the stressed Si layer 11. Butthis diffusion effect may be desirable in certain other cases, and theparameters may be suitably controlled to obtain this result. Thus,diffusion may be controlled in such a way that the Ge species aredistributed uniformly throughout both layers 2 and 5 to form a uniqueSi_(1-x)Ge_(x) layer with a substantially uniform Ge concentration. Adiscussion of the latter point can be found in U.S. Pat. No. 5,461,243,at column 3, lines 48-58.

With reference to FIGS. 4 a-4 i, and more particularly to FIGS. 4 c and4g, a method is illustrated that generally is the same as the onedescribed with reference to FIGS. 1 a-1 i, except that:

-   -   Only part of the layer 3 is transformed into a glassy layer 4;    -   The surface layer 1B is not transformed into a second glassy        layer 8.

In fact, this method includes a step identical to the one described withreference to FIG. 3 c, forming an inserted layer 5 (see FIG. 3 c), and astep identical to the one described with reference to FIG. 2 g, formingan intermediate layer 9 (see FIG. 2 g). The means for forming both ofthese layers 5 and 9, as well as the possibilities for developing theirstructure and their effect on the final structure, are thereforesubstantially the same as those described with reference to FIGS. 2 a-2i and to FIGS. 3 a-3 i.

With reference to FIGS. 5 a-5 h, and more particularly to FIGS. 5 b and5d, the method is generally the same as the one described above withreference to FIGS. 1 a-1 i, except that:

-   -   with reference to step 5 b, the epitaxial Si layer 3 on the        stressed layer 2 is a very thin layer, the thickness of which is        much less than that of the stressed layer 2, typically from        about 100 to 300 Å;    -   with reference to FIG. 5 d, the glassy layer 4 is formed on the        receiving substrate 7.

The Si layer 3 will thus enable the overlying SiGe stressed layer 2 tobe protected from Ge diffusion, external contamination and uncontrolledpotential reactivation of its surface. A suitable surface finishingmethod can be applied to the Si, whereas such suitable methods do notexist for SiGe. These finishing techniques (already detailed above) mayprovide good bonding with the receiving substrate 7.

With reference to FIG. 5 d, according to a first embodiment, the glassylayer 4 is formed before bonding onto the receiving substrate 7. Thematerial forming the glassy layer 4 is such that it becomes viscous at aviscosity temperature T_(G). Advantageously, the material of the glassylayer 4 is one of the following materials: BPSG, SiO₂, SiON. This firstembodiment for forming the glassy layer 4 on the receiving substrate issimilar to the first embodiment for forming the glassy layer 4 on thestressed layer 2 as described above with reference to FIG. 1 c. Thus,for example, oxidization of the Si surface of the receiving substrate 7may form a SiO₂ glassy layer 4. It is important that the formation ofthe glassy layer 4 and the bonding of the glassy layer 4 with thestressed layer 2 be completed before Ge diffusion, contamination anduncontrolled reactivation of the surface of the stressed layer 2,especially if the stressed layer 2 remains at a high temperature.

According to a second embodiment for forming the glassy layer 4 on thereceiving substrate, deposition of atomic species is applied by meansfor depositing atomic species on the receiving substrate 7. In a firstcase, the atomic species consisting of glassy material such as SiO₂ willbe directly deposited. In a second case, the following operations willbe applied:

-   -   deposition of amorphous Si atomic species in order to form an        amorphous Si layer, and then:    -   thermal oxidization of the amorphous Si layer to thereby form a        SiO₂ glassy layer 4.

Whichever deposition case is selected, deposition of the atomic speciesshould be achieved before Ge diffusion, contamination and uncontrolledreactivation of the surface of the stressed layer 2, and especially ifthe stressed layer 2 remains at a high temperature.

With reference to FIGS. 5 e, 5 f, 5 g and 5 h, the same conditions andthe same configurations as those discussed above with reference to FIGS.3 f, 3f, 3h and 3i apply, whereby the referenced layer 5 becomes thereferenced layer 3 in the present method. In particular, during the heattreatment for relaxation the stressed layer 2 becomes at least apartially relaxed layer 2′, and the inserted layer 3 then becomes astressed inserted layer 3′.

With reference to FIG. 5 g, the formed structure consists of relaxedSi_(1-x)Ge_(x), a stressed Si layer, a glassy layer 4, and a receivingsubstrate 7. This structure 30 is a SG/SOI structure, if the glassylayer 4 is electrically insulating, such as for example a SiO₂ glassylayer 4. The relaxed Si_(1-x)Ge_(x) layer 2′ may then be optionallyremoved, for example by selective chemical etching based onHF:H₂O₂:CH₃COOH (selectivity of about 1:1,000) in order to finally havea structure consisting of a stressed Si layer, a glassy layer 4, and areceiving substrate 7, as shown in FIG. 7. This structure is a stressedSOI structure, if the glassy layer 4 is electrically insulating, such asfor example a SiO₂ glassy layer 4.

Instead of applying chemical etching, it is possible to grow a Si layer,with reference to FIG. 5 h, by resuming growth on the relaxed layer 2′in order to form a stressed Si layer 11, substantially identical to thatshown in FIG. 5 h. The structure 40 consists of a stressed Si layer, arelaxed Si_(1-x)Ge_(x) layer, a stressed Si layer, a glassy layer 4, anda receiving substrate 7. This structure 40 is a Si/SG/SOI structure, ifthe glassy layer 4 is electrically insulating, such as for example aSiO₂ glassy layer 4.

If the heat treatment for relaxing the stresses of the stressed layer 2is carried out at a higher than standard temperature and longer than astandard duration for which Ge diffuses into Si, then the Ge containedin the stressed layer 2 may diffuse into the stressed inserted layer 3′.This is why it is preferable to apply relaxation of the stressed SiGelayer 2 before resuming epitaxial growth of the stressed Si layer 11.However, in certain cases, this diffusion effect, if it is suitablycontrolled, may be desired.

Thus, diffusion may be controlled in such a way that the Ge species areuniformly distributed throughout both layers 2 and 5, forming a uniqueSi_(1-x)Ge_(x) layer with a substantially uniform Ge concentration. Adiscussion of this point can be found in U.S. Pat. No. 5,461,243 atcolumn 3, lines 48-58.

With reference to FIGS. 6 a-6 h, and more particularly to FIG. 6 f, themethod is generally the same as the one described with reference toFIGS. 5 a-5 h, except for the step for transforming the surface layer 1Binto a second glassy layer 8, which is applied to transform only aportion of the surface layer 1B. Thus, a portion of the Si surface layer1B remains inserted between the second glassy layer 8 and the stressedlayer 2, forming an intermediate layer 9. With reference to FIG. 6 g,this intermediate layer 9 is preserved after the heat treatment forrelaxing the stressed layer 2. Advantageously, this intermediate layer 9has a thickness less than the stress critical thickness, so that it isstressed subsequently by the relaxed layer 2′.

With reference to FIG. 6 h, it is possible to resume growth of a Silayer on the intermediate layer 9 so as to form a stressed Si layer 11,substantially identical with that of FIG. 5 h. A smoothing step for thegrowth surface by means of one of the techniques already discussed abovemay be applied prior to growing silicon, in order to enhance the qualityof the crystal growth to be applied.

If the heat treatment for relaxing the stresses of the stressed layer 2is carried out at a temperature and for a duration higher than astandard temperature and longer than a standard duration, wherein Gediffuses into Si, then Ge contained in the stressed layer 2 may diffuseinto the intermediate layer 9 or into the inserted layer 3. This is whyit is preferable to apply the relaxation of the stressed SiGe layer 2before resuming epitaxial growth of the stressed Si layer 11. However,in certain other cases, this diffusion effect, if it is suitablycontrolled, may be desired. Thus, diffusion may be controlled so thatthe Ge species are uniformly distributed throughout both layers 2, 3 and9, forming a unique Si_(1-x)Ge_(x) layer with a substantially uniform Geconcentration. A discussion of this point can be found in U.S. Pat. No.5,461,243 at column 3, lines 48-58.

Steps for making components can be integrated according to any of thesix methods described above, or by equivalents thereof. Thus,preparation steps for making components may be applied during the methodat the stressed SiGe layer 2 of the structure with reference to FIGS. 1g, 2 g, 3 g, 4 g, 5 f or 6 f, at the relaxed or pseudo-relaxed SiGelayer 2′ of the SGOI structure with reference to FIGS. 1 h, 2 h, 3 h, 4h, 5 g or 6 g, or in the stressed Si layer 11 of the Si/SGOI structurewith reference to FIGS. 1 i, 2 i, 3 i, 4 i, 5 h or 6 h. Preferably,these preparation steps will be achieved with the glassy layer 8 alwayspresent in the structure, the latter protecting the underlying layers,and especially the stressed layer 2 or the relaxed layer 2′, both inSiGe. For example, local treatments may be undertaken for etchingpatterns in the layers through the glassy layer 8, for example bylithography, photolithography, reactive ion etching, or any otheretching technique with pattern masking.

In a particular case, patterns such as islands can be etched into theSiGe stressed layer 2 in order to contribute to proper relaxation of thestressed layer 2 during the subsequent application of the relaxationheat treatment.

One or several steps for making components, such as transistors, in thestressed Si layer 11 (or in the relaxed SiGe layer 2′ if the latter isnot covered with a stressed Si layer 11) may be applied, preferably at atemperature less than T_(G) (so as not to change the stress ratio of therelaxed layer 2′ and the stressed layer 11).

In a particular method according to the invention, steps for making thecomponents are applied during or in continuity with the heat treatmentfor relaxing the stressed SiGe layer 2.

In a particular method according to the invention, the step forepitaxial growth of the stressed Si layer is applied during or incontinuity with the steps for making the components.

The techniques described in the invention are provided by way ofexample, but are by no means limited, because the invention may extendto all types of techniques that could apply a method according to theinvention.

One or any epitaxial growth processes may be applied onto the finalstructure (structure 30 or 40 taken with reference to FIGS. 1 h, 1 i, 2h, 2 i, 3 h, 3 i, 4 h, 4 i, 5 g, 5 h, 6 g, 6 h), such as epitaxialgrowth of a SiGe or SiGeC layer, or of a stressed Si or SiC layer, orsuccessive epitaxial growths of SiGe or SiGeC layers and of alternatelystressed Si or SiC layers in order to form a multilayer structure.

Upon completion of the final structure, finishing treatments mayoptionally be applied, including an annealing step, for example.

The present invention is also not limited to a SiGe stressed layer 2,but also extends to forming the stressed layer 2 in other types ofmaterials of the III-V or II-VI type, or other semiconductor materials.

In the semiconductor layers discussed in this document, otherconstituents may be added thereto, such as carbon with a carbonconcentration in the relevant layer substantially less than or equal to50% or, more particularly with a concentration less than or equal to 5%.

1-20. (canceled)
 21. A method for relaxing a layer of a strainedmaterial on a substrate which method comprises: providing an elasticallystressed layer on a first substrate; providing a first glassy layer onthe stressed layer or upon a second substrate; bonding the first andsecond substrates together with the stressed layer and first glassylayer therebetween; removing the first substrate to obtain a structurecomprising the stressed layer, first glassy layer and second substrate;providing a second glassy layer on the stressed layer; and heat treatingthe structure at a temperature close to or higher than the viscositytemperature of one or both of the glassy layers to convert the stressedlayer to a relaxed or pseudo-relaxed layer.
 22. The method of claim 21,wherein the heat treating temperature is about 1150 to 1500° C.
 23. Themethod of claim 21, wherein the heat treating temperature is about 1150to 1200° C.
 24. The method of claim 21, wherein the stressed layer isprovided by growing the layer on the first substrate.
 25. The method ofclaim 21, wherein the first glassy layer comprises a viscous materialhaving an associated viscosity temperature, and the heat treating isconducted at or above the viscosity temperature.
 26. The method of claim21, wherein the second glassy layer is provided by removing a portion ofthe first layer and leaving a surface layer of the first substrate onthe structure, applying a controlled treatment to transform at least aportion or all of the surface layer to a viscous material having anassociated viscosity temperature, and the heat treating is conducted ator above the viscosity temperature.
 27. The method of claim 26, whichfurther comprises growing a further layer on the structure.
 28. Themethod of claim 27, which further comprises removing the second glassylayer before growing the further layer.